SHADOWLANDSQuestfor Mirr or Matter

in the Universe

SHADOWLANDSQuestfor Mirr or Matter

in the Universe

Robert Foot

foot@physics.unimelb.edu.auSchoolof Physics

University of MelbourneVictoria 3010Australia

Shadowlands: Quest for Mirror Matter in the Universe

Copyright © 2002 Robert Foot All rights reserved.

Universal Publishers / uPUBLISH.com Parkland, Florida • USA • 2002

ISBN: 1-58112-645-X (paperback)

ISBN: 1-58112-644-1 (ebook)

www.uPUBLISH.com/books/foot.htm

The picture on the cover shows the crab nebula–the remnants of a star which exploded in 1054.This photograph was

taken at the European Southern Observatory. (Credit: FORS Team, 8.2-metre VLT ESO).

A CIP catalog record for this book is available from the Library of Congress.

Preface

My purposein writing this book is two-fold. First, many non-specialistsaskmeto explainthemirror matterideaandthescientificevidencefor it. Second,scienceis so specializedthesedaysthatmany peoplewhoknow a lot aboutonefield oftenknow little aboutanother. Mirror matter, if it exists, would leadto ratherimportantimplicationsfor severalscientificfields,including: particlephysics,astrophysics,cosmology, meteoriticsandplanetaryscience.Thus,itseemedto methataninterestingchallengewouldbeto write abookexplaining themotivation for mirror matterandits evidencewhichcouldusefullyserve thesetwo communities(thatis, bothspecialistsandnon-specialistsalike). Sucha venture,though,is not withoutrisks of variouskinds. Let me stateat the outsetthat the mirrormatterideais not establishedfact; it is anexampleof cutting-edgesciencein progress.It is my hopethat peoplewho readthis bookwill be infectedby, or at leastunderstand,my enthusiasmfor thissubject,andwhy I think it is oneof themostinterestingquestionsinscienceat themoment.

Theprocessof writing this bookgave metheopportunityto re-think many of theoriginalarguments.Some‘gaps’in my knowledgewerefilled in, anda few new directionsexplored.Somematerialisthereforecompletelynew, althoughmostof it hasappearedin thetechnicalscientificliteraturepreviously. I have only cited this sci-entific literaturesparingly, but neverthelessI have endeavouredtoproperlycreditthepeopleresponsiblefor themainoriginal ideas.

It seemsonly yesterdaythat I learnedasa studentthat mirrorreflectionsymmetrywasnot respectedby the fundamentalinterac-tions of nature. Electronsandotherelementaryparticlesare, in asense,‘left-handed’.Althoughmostscientistshave simply cometoacceptthatGodis ‘left-handed’,somehow it alwaysbotheredme....

ii Preface

Onesunny afternoonin May 1991a ratherremarkablethoughtoccurredto me. While playing with an unrelatedidea,it suddenlystruckmethattherewasasubtleyetsimpleway in whichmirror re-flectionsymmetrycouldstill exist. Nature’s mirror couldbeunbro-ken if eachtypeof ordinaryparticlehasa shadowy mirror partner.Theleft-handednessof theordinaryparticlescouldthenbebalancedby the right-handednessof the mirror particles.So thereyou haveit, mirror reflectionsymmetrycanexist but requiressomethingpro-foundly new. It requirestheexistenceof a completelynew form ofmattercalled‘mirror matter’.

At first, it seemedtoo fantasticto really exist. Yet,over thelastfew yearsit appearsthatalmosteveryastrophysicalandexperimen-tal predictionof themirror mattertheoryhasactuallybeenobservedby observationsandexperiments:Thereis fascinatingevidenceformirror matterin the Universefrom astronomicalobservationssug-gestingthatmostof our galaxyis composedof exotic darkmaterialcalled‘dark matter’. Recentparticlephysicsexperimentshave re-vealedunexpectedpropertiesof ghostlyparticlescalled‘neutrinos’andweird matteranti-matteratoms. This unexpectedbehaviour isexpectedif mirror matterexists. Most remarkableof all is theevi-dencethatour planetis frequentlybombardedby mirror matteras-teroid or cometsizedobjects,causingpuzzlingeventssuchasthehuge1908Siberianexplosionwhich felled morethantwo thousandsquarekilometresof nativeforestswithoutleaving asinglemeteoritefragmentbehind! AltogetherI will discussseven major puzzlesinastrophysicsandparticlephysicseacharguing in favour of themir-ror matterhypothesis.Thereareindeedsevenwondersof themirrorworld...

New datafrom currentandfutureexperimentswill keepcomingin even as this book is being printed. Unfortunately, I am not afortuneteller anddo not know what thesefuture experimentsandobservationswill find. However, I canpredictwhatthey will find ifmirror reflectionsymmetryandhencemirror matterexists.Thecasefor mirror matterwill thereforeeitherstrengthenor weakenasnewdatacomesin andfuture experimentsaredone. In the meantime,I adviseyou to sit back, relax and let me take you on a journeyexploring oneof theboldestscientificideasever proposed.

Preface iii

No scientistworks in isolationand I am no exception. I havehadfruitful collaborationson mirror matterwith a numberof verycreative people,including Sergei Gninenko, SashaIgnatiev, HenryLew, ZurabSilagadze,RayVolkasandT. L. Yoon. I have enjoyedinterestingcorrespondenceon someaspectsof this subjectwithSergei Blinnikov, ZdenekCeplechaandAndrei Ol’khovatov. In ad-dition, I wouldliketoacknowledgeinvaluablesupportovertheyearsfrom many friendsandcolleaguesincluding in particular, PasqualeDi Bari, JohnEastman,GregFilewood,DaveHowland,GirishJoshi,Matthew Tully, andNick Whitelegg. I amalsogreatfulto many oftheabovepeople,andalsoJaciAndersonandGlenDeenfor provid-ing mewith usefulcommentson themanuscriptandTony Nguyenfor helpingwith thecover.

Of course,I thankmy family mostof all. It is to themthat Idedicatethisbook.

RobertFootAugust2001

* * *

.

for CarolynandJames

* * *

Contents

Part I: Why Mirror Matter?

1. Introduction 3

2. ElementaryParticlesandForces 17

Part II: Evidencefor Mirror Matterin theUniverse

3. Discoveryof Mirror Stars? 39

4. Discoveryof Mirror Planets? 67

Part III: Evidencefor Mirror Matterin theLaboratoryandSolarSystem

5. Mirror MatterandPositronium 107

6. Mirror MatterandtheTunguskaEvent 137

Part IV: Evidencefor Mirror Matterfrom DeepUnderground

7. TheMysteryof theDisappearingNeutrinos 175

8. More MissingNeutrinos 205

9. Reflectionson theMirror World 221

Furtherreading

Notes

* * *

There aremore thingsinHeavenandEarth,Horatio, thanare dreamtof in your philosophy.

William Shakespeare– Hamlet.

PART I

Why Mirr or Matter?

Chapter 1

Intr oduction

Shortly beforehis deathin 1727, IsaacNewton reflecteduponhislife andwrote

�:

I don’t know what I may appearto the world, but, as tomyself I seemto have beenonly like a boy playing on theseashore,and diverting myself in now and then finding asmootherpebbleor a prettiershell thanordinary, whilst thegreatoceanof truth lay all undiscoveredbeforeme.

More recently in StephenHawking’s a brief history of time, it iswritten

�:

I still believe that therearegroundsfor cautiousoptimismthatwe may now be nearthe endof the searchfor the ulti-matelawsof nature.

The contrastbetweenthe currentLucasianProfessorand the for-merholderof thatpositionis striking. Hawking is not alonein hisprophecy. It hasbeenrepeatedwith monotonousregularitysincethedaysof Maxwell (1865).Onedayit maycometrue,but thatdayis alongwayoff. I believethatarevolutionin sciencemaybeimminent.In fact, over the last decade,remarkableevidencefrom astronomy(studiesof the very big) to studiesof the elementaryparticles(thevery small) suggestthat a completelynew type of matterexists –‘mirror matter’. Thebestideasin scienceareusuallyvery simple,

3

4 Introduction

andfortunatelymirror matterbelongsto thiscategory. I believe thatthe ideasandtheevidencecanbeappreciatedby anyoneinterestedin science.

In the processof uncovering mirror matterwe will encountermany recentandunexpecteddiscoveries,including:� Invisible starswhich reveal their presenceby gravitationally

bendingthelight from moredistantstarsbehindthem. I willarguethattheseinvisiblestarsaremadeof mirrormatterwhichcansimply explainwhy we don’t seethem.

� Planetsorbiting nearbystarswhich areeight timesclosertotheir star than the distanceMercury orbits the Sun. I willsuggestthattheseunexpectedplanetsareexpectedif they aremadeof mirror matter.

� Bizarre, apparentlyfree-floatingplanetswanderingthroughspace. They can be more naturally interpretedas ordinaryplanetsorbitingmirror stars,but I couldbewrong!

� Strangeandunexpectedpropertiesof elementaryparticlessuchastheghostlyneutrinos.Theseparticlesareemittedfrom theSunandin otherprocesses.However, half of themaremiss-ing! The missingneutrinosmay have beentransformedintomirror neutrinosasI will explain.

� I will alsodiscussastrangeclassof ‘meteoriteevents’suchasthe hugeSiberian1908explosionandothersimilar suchex-plosions. Thereis evidencethat theseexplosionsarecausedby the randomcollisionsof our planetwith orbiting ‘mirrormatterspace-bodies’.Most remarkableof all is the realpos-sibility thatmirror matterremnantsmaystill bein thegroundtoday! Needlessto saythepossibleusesof this new typeofmatterarenotevenimagined...

By the way, this is a (generally)seriousscientificbook. However,unlike other ‘seriousscientificbooks’ this book doesnot claim toreveal the ‘mind of God’. In fact,not many ridiculouslygrandiosestatementswill be madeat all. Rather, it is simply a book aboutmirror reflectionsymmetry– andits far reachingimplications.

Introduction 5

Symmetryis a word frequentlyusedin everydaylanguageandweareall awareof whatit means.Examplesof symmetricalobjectsabound:flowers,butterflies,snowflakes,soccerballsandsoon... Infact, assomeof theseexamplesillustrate,symmetryis often asso-ciatedwith beautyandvice versa.It is perhapsnot surprisingthenthat symmetryplaysa pivotal role in our understandingof theele-mentaryparticlesandtheir forces,but let mestartat thebeginning.

Therearemany distinct typesof symmetry. The symmetryofa mushroomis completelydifferent to the symmetryof a butterflywhich in turn is completelydifferent to the symmetryof a soccerball. A butterfly is an exampleof the most familiar symmetry–‘left-right’ symmetry. This symmetryoccurswhentwo equalpor-tions of a whole are the mirror imageof eachother. For obviousreasons,this symmetryis alsocalled‘mirror’ symmetry. A soccerball is anexampleof anothertypeof symmetry– rotationalsymme-try. In fact,it is anexampleof anobjectwith threedimensionalro-tationalsymmetrybecauserotationsaroundany axisdo not changethe appearanceof the ball. Finally a straightfenceor railway lineareexamplesof objectswhich displayanothertypeof symmetry–translationalsymmetry. A railway line or fencelooks the sameaswe movealongit.

Fortunatelythe everydayusageof the conceptof symmetryisexactly the sameas its technicalusagein science. Although it isoftenusefulto describesymmetryin amathematicalway– thisneednot concernus. Herewe needonly discussthe ideasandconceptswhich is enoughto glimpsethe beautifulworld of the elementaryparticlesandtheir interactions.

Most peopleareaware that ordinarymatter: you, me andev-erythingelsewe see,exceptlight itself, is composedof atoms.Al-thoughatomsare very tiny, approximatelyone ten millionth of amillimetre in size,they arestill not themostfundamentalbuildingblocksof matter. Atomsarenotelementaryentities.EachindividualAtom is madeup of electronsanda compactnucleus,which in turnis madefrom protonsandneutrons.Thereareabout100 differenttypesof atomsdependingon thenumberof electronsthatthey con-tain. Thescienceof atoms,how they interactwith eachotherto formmoleculesandhow differentmoleculesinteractwith eachotheris of

6 Introduction

coursethescienceof chemistry. However, we will not be involvedso muchwith chemistrybut with the mostfundamentalof the sci-ences– physics. One thing that physicsis concernedwith is themostbasicquestionsthat canbeasked. For example,whatarethepropertiesof the elementaryparticles:protons,neutrons,electronsfrom whichall matteris made?How do theseparticlesinteractwitheachotherandwith light?

Onethingthathasbeenlearnedovertheyearsis thattheinterac-tionsof elementaryparticlesdisplaya varietyof symmetries.Someof thesesymmetriesarequite familiar suchasrotationalsymmetryand translationalsymmetry. Thus, the laws of physicsremainthesamewhetherwearein Melbourneor in Moscow, whichmeansthatRussianphysicstext booksare useful in Australia and vice versa(afterthey aretranslated...).In additionto translationsin space(andtranslationsin language!)we canimaginetranslationsin time. Thelaws of physicsarethe sametodayasyesterdayor even a centuryago, however our knowledgeof theselaws generallyimproves astime goesby. Hence,physicstext booksare not the sametodayasa centuryago,yet the laws of physicsare the same. Therearestill othermoreabstractsymmetriesof theelementaryparticleinter-actions. Thesearecalled‘Lorentz symmetry’and‘gaugesymme-try’, which areneverthelessquiteelegantandnaturalonceyou getto know them.

Progressin scienceis rarelyasmoothcomfortablejourney. Rapidprogressgenerallyoccursin brief intervalsusuallythroughnew andunexpectedexperimentalresultsandsometimesthroughnovel the-oretical ideas. Of courseprogressis most rapid when theoryandexperimentmove togetherin harmony. Oneof themostremarkabletheoreticalideasof the

�������centurywas the discovery of relativ-

ity theory in 1905 by Albert Einstein. Spaceand time were uni-fied with time becomingthe fourth dimension.Einsteinsuggestedthat the laws of physicswere symmetricalunderrotationsin thisfour dimensionalspace-time,ratherthanjust the threedimensionsof space.Thepredictionsof this theory, suchasmoving clocksmustrunmoreslowly, havebeenexperimentallyverifiedwith tremendousprecision. This is possiblebecauseEinstein’s theorynot only tellsus that moving clocksrun moreslowly, but it tells us exactly how

Introduction 7

muchmoreslowly! This four dimensionalrotationalsymmetryofspace-timeis called‘Lorentzsymmetry’* .

There are four known fundamentalforces in nature: gravity,electromagnetism,weakandstrongnuclearforces.Gravity is quitefamiliar to mostof us. It keepsour feeton theground,it keepsourplanetandall theotherplanetsin our solarsystemin orbit aroundtheSunandit keepstheSunin orbit aroundthecentreof ourgalaxy.Electromagnetismis nolessimportant– while it is gravity thatholdsus down, it is electromagnetismthat stopsus from falling throughthe floor. It is also the force responsiblefor electricity andmag-netism.While theweakandstrongnuclearforcesarelessfamiliar,they areneverthelessequallyfundamentalandimportantastheothermore familiar forces. For example, the weak and strongnuclearforceprovidestheenergy whichpowerstheSun,withoutwhichourplanetwouldbetoocold to sustainlife.

Todayweknow thatthreeof theseforces,electromagnetism,theweakandstrongnuclearforcesare,mathematically, verysimilarandfairly well understood.Gravity, on theotherhand,is quitedifferentand its relation to the other forcesis somewhat mysterious. Onereasonis thatgravity canbedescribedin geometricaltermsasacur-vatureof four dimensionalspace-timewhile the otherthreeforcesaredescribedin termsof symmetriesonanabstract‘internal’ space,whichis nothingto dowith ordinaryspace-timethatweknow about.Thesepeculiarsymmetriesof theelectromagnetic,weakandstrongnuclearforcesarecalled‘gaugesymmetries’.

Evidently, symmetriesareratherimportantin understandingtheelementaryparticlesand their forces. However, it is pertinenttorecall that thesesymmetrieswerenot alwayssoobvious. I have al-readymentionedthecaseof Lorentzsymmetry– theratherabstractidea that spaceand time can be treatedmathematicallyas a fourdimensionalspace-time.In fact,afterthediscovery of relativity the-ory andLorentzsymmetry, an EnglishPhysicistcalledPaul Diracuncoveredabig problem.In thelate1920’s Diracnoticedthatami-croscopicmathematicaldescriptionof the electronconsistentwith

* In additionto Albert Einstein’sinsight,importantcontributionsto therelativitytheoryweremadeby others,including:HendrikLorentz,HermannMinkowski andHenri Poincare.

8 Introduction

Lorentzsymmetrywasnot possible,unlesssomethingcompletelynew existed.Nothingshortof a new form of matterwasrequiredtoreconcileEinstein’s relativity theorywith the quantummechanicaltheoryof theelectron.Thisnew form of matter, called‘anti-matter’wastherebytheoreticallypredictedto exist.

Specifically, Diracpredictedthatin additionto theparticlesthatmakeupordinarymatter– theelectrons,protonsandneutrons,anti-particlescalled ‘positrons’ (or anti-electrons),‘anti-protons’ and‘anti-neutrons’shouldall exist. The symmetryrequiredeachtypeof anti-particleto have the samemassas the correspondingpar-ticle. Positronsandanti-nuclei(madefrom anti-protonsandanti-neutrons)shouldform ‘anti-atoms’. However, anti-particlesshouldannihilatewhenthey meetordinaryparticlesproducinggammarays(high frequency light). History tells usthatexperimentsshortlyfol-lowed which dramaticallyconfirmedthe existenceof Dirac’s anti-particles.First, thediscovery of thepositronin 1932,andlater, thediscovery of anti-protonsin the 1950’s. Anti-matter is not sciencefantasybut sciencereality. Clearly, the ideaof symmetrycanhaveremarkableimplications.

This bookthough,is concernednot with Lorentzsymmetrybutwith left-rightor mirror reflectionsymmetry. Letusnow briefly lookat thehistoryof thissymmetry. Before1956physicistshadassumedthat thelaws of physicsweresymmetricunderleft-right symmetry.This would meanthat for every fundamentalmicroscopicprocessthat is known to occur, themirror imageprocessshouldalsooccur.In factleft-right symmetryis suchafamiliarandplausiblesymmetryof naturethatit wasneverseriouslyquestioneduntil variousexperi-mentalpuzzlesbeganappearingin the1950’s. Thesepuzzlesled T.D. LeeandC. N. Yangto suggestthat theweaknuclearforcedoesnot display left-right symmetry. They proposedan experimenttodirectly testtheideainvolving the -decayof anunstableisotope...

At the time, mostscientistsdidn’t expectthatmirror symmetrycould really bebroken. Theprevailing scepticismwassummedupby WolfgangPauli whenhewrotein December1956 :

I amhoweverpreparedto betthattheexperimentwill bede-cidedin favourof mirror invariance.For in spiteof YangandLee,I don’t believe thatGodis aweakleft-hander.

Introduction 9

However, Pauli wasnotsofoolishasto let hisbeliefsgetin thewayof science.He did agreethatexperimentsshouldbedoneto checkit � :

I believein reflectioninvariancein contrasttoYangandLee...Betweenbelieving andknowing is adifferenceandin thelastendsuchquestionsmustbedecidedexperimentally.

The experimentsuggestedby Lee andYangwasperformedin1957by C. S.Wu andcollaborators.In thisexperimentanumberofcobalt-60atomswerecooleddown to nearabsolutezeroKelvin (thelowestpossibletemperature)andplacedin a strongmagneticfield.Cobalt-60is anunstableisotope.Ordinarily, Cobalt-60decaysemit-ting an electronwith any directionequally likely. However, undertheseextremeconditions,the electronsshouldbe equally likely toemergefrom thetwo polesof themagneticfield – if thefundamen-tal decayprocessdisplayedmirror symmetry. Yet, it wasobservedthat moreelectronscameout from onedirectionthanthe other. Ifwe observed only onenuclei decayingwe could not sayanything.Mirror symmetrydoesnot meanthateachsingleinteractionor de-cayprocessis thesameasits mirror image– it is not. Mirror sym-metry meansthat the mirror imageprocesscan occur and shouldoccurwith equalprobability. Therefore,by observinga largenum-berof decaysof Cobalt-60we caneasilydeterminewhethermirrorsymmetryis violated.Theremarkableconclusionwasthat thefun-damentallaws of physicsappearto be ‘left-handed’. This is reallyverystrange.Everyotherplausiblesymmetry, suchasrotationalandtranslationalsymmetry, arefoundto bemicroscopicsymmetriesofparticleinteractions.Cannaturereally beleft-handed?

Are they, the fundamentallaws of physicsthat is, really left-handedor do they only appearto be left-handed?RememberourearliercommentsaboutLorentzsymmetry. At onetime this sym-metry did not appear to be a symmetryat all. This was becauseanti-matterhadyet to bediscovered.Only whenyou have particlesand anti-particlesis it possibleto write down a consistentmicro-scopictheoryfor theinteractionsof theelectron,protonandneutronwhich respectsLorentzsymmetry. Remarkably, it turnsout thatit isstill possiblefor particleinteractionsto besymmetricundermirror

10 Introduction

or left-right symmetry. JustasLorentzsymmetryrequiredthe ex-istenceof anti-matter, left-right symmetrycanexist if andonly if anew form of matterexists– mirror matter.

Often,it seemsthatnatureis moresubtleandbeautifulthenfirstimagined.It couldbethatnature’s mirror is of amoreabstractkind.Imaginethat for eachtype of ordinaryparticle thereis a separate‘mirror particle’. That is, not only do we have photons,electrons,positrons,protonsetc., but also mirror photons,mirror electrons,mirror positrons,mirror protonsetc.Wecanimaginethatin nature’smirror notonly spaceis reflectedbut alsoparticlesarereflectedintothesemirror particles.Therelationshipbetweenordinaryandmirrormatteris somewhat like therelationshipbetweentheletters‘b’ and‘d’. The mirror imageof ‘b’ is the letter ‘d’ andthe mirror imageof ‘d’ is the letter ‘b’. Thus,while neither‘b’ nor ‘d’ is symmetric(in a sensethey eachhave the oppositehandedness),together‘bd’is in factmirror symmetric,with thetwo lettersinterchangingin themirror image� . Try it with a mirror andsee!Still, themirror reflec-tion of an objectappearsvery similar to the original. It is perhapsnot surprising,therefore,that the propertiesof the mirror particlesturnout to beverysimilar to theordinaryparticles.For example,themirror particlesmusthave thesamemassandlifetime aseachof theordinaryparticles,otherwisethemirror symmetrywouldbebroken.

In somewaysmirror particlesresembleanti-particles.However,thereis a crucialdifference.Unlike anti-particles,themirror parti-clesinteractwith ordinaryparticlespredominatelyby gravity only.The threenon-gravitational forcesact on ordinaryandmirror par-ticles completelyseparately. For example,while ordinaryphotons(that is, ordinarylight) interactwith ordinarymatter(which is justthe microscopicpictureof the electromagneticforce), they do notinteractwith mirror matter. Similarly, the ‘mirror image’ of thisstatementmustalsohold, that is, themirror photon(that is, mirrorlight) interactswith mirror matterbut doesnotinteractwith ordinarymatter. Theupshotis thatwecannotseemirror photonsbecausewearemadeof ordinarymatter. Themirror photonswouldsimplypassright throughuswithout interactingatall!

The mirror symmetrydoesrequirethoughthat the mirror pho-tonsinteractwith mirror electronsandmirror protonsin exactly the

Introduction 11

samewayin whichordinaryphotonsinteractwith ordinaryelectronsandordinaryprotons.A directconsequenceof this is thata mirroratommadefrom mirror electronsandamirror nucleus,composedofmirror protonsandmirror neutronscanexist. In fact,mirror mattermadefrom mirror atomswould alsoexist with exactly thesamein-ternalpropertiesasordinarymatter, but would becompletelyinvis-ible to us! If you hada rock madeof mirror matteron your hand,itwouldsimplyfall throughyourhandandthenthroughtheEarth,andit wouldenduposcillatingabouttheEarth’scentre* . Wecansafelyconcludethat if therewasa negligible amountof mirror matterinour solarsystem,we would hardly be awareof its existenceat all.Thus,theapparent left-right asymmetryof the laws of naturemaybedueto thepreponderanceof ordinarymatterin our solarsystemratherthandueto a fundamentalasymmetryin thelaws themselves.

Do mirror particlesreally make the laws of physicsleft-rightsymmetric?Let usconsidera simpleandlight-hearted‘thoughtex-periment’involving againtheCobalt-60decay. Imaginetherewasamirror planetorbiting a mirror starin a distantpartof our Universe(note that thereis only one space-time– thereis no ‘mirror Uni-verse’).Let’scall thishypotheticalplanet‘Miros’. Miros is aplanetmadeof mirror matter– atomscomposedof mirror electronsandmirror protonsandmirror neutrons.Miros is somewhatdifferenttoEarththough.It’s a bit smallerwith deeperoceans,but thereis lifeonMiros. Thepeopleof Miros areabit strange,they haveverylargefeetandonly haveoneeye– but they areveryhappy. They havewiseleaderswhowouldnever dreamof puttingnuclearmissilesin spaceandthey realisedveryearlytheimportanceof reducinggreenhousegases.On Miros a football teamcalled ‘Collingwood’ often winsthefootball. Thus,Miros isn’t muchlikeEarthwhich just illustratesthatmicroscopicsymmetryof particleinteractionsdoesnottranslateinto a macroscopicsymmetry.

* LaterI will discussthepossibilitythatanew typeof interaction(or force)couldexist couplingordinarymatterto mirror matter. If this is thecase,it mayactuallybepossibleto pick upamirror rock,althoughit wouldstill beinvisible. Clearly, theconsequencesof suchaforceareveryimportantandit will beconsideredin chapter5. However, in orderto keepthis introductorydiscussionassimpleaspossible,thispossibilityhasbeenignored.

12 Introduction

Anyway, our mirror matter friends on Miros realisedthe im-portanceof purescience;their wisegovernmentalwaysmadesurethatfinancialsupportwasgivento thosemirror scientistswhohadaresearchrecordconsistingof interestingandinnovative ideas.OnedaysomeoneonMiros hadtheideathatthey shouldtestwhetherthefundamentallawsof naturearemirror symmetricor not. Sothey setup their Cobalt-60experimentwith a similar experimentalsetup aswasdoneby peoplehereonEarthin 1957.But whatthey foundwassomethingquitedifferent.They foundthemirror imageresult.Thatis, they foundthatthemirror electronsweremostlyemittedfrom thedecayingCobalt-60mirror nucleusin theoppositedirectionaswasfoundhereonEarth.Ourmirror friendsonMiros concludedthatthelaws of physicswereright-handed.

Thelawsof physicscannotbothbeleft-handedandright-handed.Ordinaryparticlesform a left-handedsector, mirror particlesforma right-handedsector. Taken together, neitherleft nor right is sin-gledout,sinceordinaryandmirror particlesareotherwiseidentical.(This is muchlike theletters‘b’ and‘d’; ‘b’ representstheordinaryparticlesand interactionsand ‘d’ the mirror particlesand interac-tions).However, if mirror particlesdon’t exist anywherein theUni-versethenthe laws of physicsareindeedleft-handed.Similarly iftheUniversewasfull of mirror particleswith noordinaryones,thenthelaws of physicswould beright-handed,but if bothordinaryandmirror particlesexist togetherthenleft-right symmetryis restored.

Thebasicgeometricpointis illustratedin thefollowing diagram.

Nature’s Mirror

The left-handsideof this figure representsthe interactionsof theknown elementaryparticles.Theforcesaremirror symmetriclike aperfectsphere,exceptfor theweakinteraction,which is represented

Introduction 13

asa left hand.Also shown is nature’s mirror - theverticalline downthe middle. Clearly, the reflectionis not the sameasthe original,signifying the fact that the interactionsof the knownparticlesarenot mirror symmetric. If therewerea right handaswell asa lefthandthenmirror symmetrywouldbeunbrokenwithout theneedfornew particles:

However, this doesn’t correspondto naturesinceno right-handedweakinteractionsareseenin experiments.

Thereare two remainingpossibilities: We caneitherchopthehandoff – but this is toodrasticandis thereforenotshown. It corre-spondsto having no weakinteractionsat all, againin disagreementwith observations. This lastpossibilityconsistsof addinganentirenew figure with the handon the otherside. Everythingis doubledeventhesymmetricpart,which is clearlymirror symmetricasindi-catedin thefollowing diagram:

It is this lastpossibilitythatmaycorrespondto nature.While themirror mattertheoryis simple,elegant,andthe idea

hasbeenknown for a long time, it is only in thepastdecadethatex-perimentalandobservationalevidencefor mirror matterhasgrownto thepoint whereastrongcasecanbemadethatit actuallyexists–andhencethemotivationfor thisbook.Theevidencefor mirror mat-ter is diverse,rangingfrom studiesof the lightestandmostelusive